The present invention relates to a drafting material which comprises a plastic support having, on at least one surface, an adhesive layer, a layer of a pigmented or clear lacquer and an antistatic top layer.
Drafting materials such as, for example, drafting films, are usually made from a plastic support of cellulose acetate, polyvinyl chloride, polypropylene or preferably polyester, in particular polyethylene terephthalate which is provided with an adhesive layer on at least one surface. The film is preferably coated with a pigmented lacquer system to produce a surface which can be marked or written on with pencil lead and india ink. The material can be equipped with a separate top layer which is applied to the layer of pigmented lacquer in order to obtain ink adherence. If a drafting film is to be used for drawing with india ink only, a transparent lacquer can be used instead of the pigmented lacquer and the top layer then contains an antistatic agent.
British Pat. No. 1,394,689 discloses a drafting material, in which a heat-curable binder system comprising polyvinyl acetate, a urea-formaldehyde or melamine-formaldehyde resin and an acid constituent is present on a polyester support, the surface of which has not been pretreated. The drafting layer adheres well to the support, but its properties with respect to writeability and ink adherence are not yet adapted to the usual technical requirements. The material does not contain an antistatic agent.
From British Pat. No. 1,222,727 a drafting layer is known, which contains a partially hydrolyzed polyvinyl lactate or glycollate as the binder, a urea-formaldehyde or melamine-formaldehyde resin as the crosslinking agent and p-toluene sulfonic acid as the catalyst. Crosslinking is performed at a temperature of 120.degree. C. during a period of approximately 20 minutes. Such treatment is, however, somewhat problematic and produces undesirable modifications of the drafting layer and the support.
Pat. No. 93,015 of the German Democratic Republic describes a method of preparing a drafting film. According to this method, a polyester film having a pretreated surface is coated with a pigmented binder matrix comprising a combination of an acrylate, an alkyd and a melamine-formaldehyde resin. The drafting film thus produced shows good adhesion of the coating and good resistance to the action of water and light. But this film also does not have the properties expected of a good drafting film, for example, in terms of the capability of accepting india inks containing water or solvents and the solvent resistance of the coating.
In German Pat. No. 16 21 988 (equivalent to British Pat. No. 1,231,407) a transparent drafting material is described which comprises a support of polyester film and a drafting layer containing silica and/or aluminum silicate as a pigment and a cured mixture of polyvinyl alcohol, a urea-formaldehyde or melamine-formaldehyde precondensate and an acrylic acid ester as a binder. When preparing this drafting material it is a disadvantage that drying and curing must be performed in two separate operations. Another disadvantage is that the material is not sufficiently resistant when it is used for writing on with hard film marking pencils and is only slightly wetted by india ink. In addition, the antistatic properties of the material are insufficient.
The drafting material which is known from European Patent Application No. 0,119,464 (equivalent to U.S. Pat. No. 4,543,316) comprises a plastic support, at least one surface of which is coated with an adhesive layer, a layer of pigmented or clear lacquer and a top layer containing an antistatic agent. This material is not yet readily applicable to special purposes, for example, in view of solvent resistance and hardness.